Electronic means providing tremolo for electrically operated musical instruments



Oct. 18, 19

P. H. Row' ELECTRONIC MEANS PROVIDING TREMOLO FOR ELECTRICALLY OPERATED MUSICAL INSTRUMENTS I Filed May 26, 1947 Osc/Wa tor muenfor Attorney Patented Oct. 18, 1949 UNITED STATES PATENT OFFICE ELECTRONIC MEANS PROVIDING TREMOLO FOR ELECTRICALLY OPERATED MUSICAL INSTRUMENTS Paul H. Rowe, Los Angeles, Calif., assignor to Maas-Rowe Electromusic Corporation, Los Angeles, Galif., a corporation of California Application May 26, 1947, Serial No. 750,414

6 Claims.

by appropriate use of audio-frequency electric currents, the wave pattern corresponding in timbre and pitch with the sounds. These electric currents in turn can be caused to actuate a sound reproducer, converting the electrical impulses into sound impulses.

It is one of the objects of this invention to provide a simple and effective means for adding tremolo effects to currents corresponding to musical sounds. and especially by the aid of electronic tubes.

It is another object of this invention to provide tremolo effects, the amplitudes of which can be very simply adjusted from zero to a maximum volume.

It is preferable to use an electronic tube oscillator operating at the desired tremolo frequency (from live to ten cycles), and to modulate an amplifier of the push-pull balanced type by cathode voltage control. It is another object of this invention to provide a system of this character in which the oscillator serves to modulate the amplifier output by the aid of a resistor common to the input circuits of the amplifier and the oscillator. By aid of such an arrangement, the intensity of the tremolo can be very readily and simply controlled, as by control of the current through a resistor common to the input circuits. It is another object of this invention to provide a simple and effective mode of controlling the current flow through the resistor.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of one embodiment of the invention. For this purpose there is shown a form in the drawings accompanying and forming part of the present specification. The form will now be described in detail illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of this invention is best defined by the appended claims.

Referring to the drawings:

H and I2.

The single figure is a wiring diagram of a system embodying the invention.

An audio frequency transformer I has a primary winding 2 which is coupled to a secondary winding 3. The primary winding 2 is connected to a source of musical sounds to which it is desired to add tremolo or vibrato eiiects.

The output to which the tremolo effects have been added, includes an output transformer 4 having a primary winding 5 and a secondary winding 6. This secondary winding 6 may be appropriately connected to an additional amplifier if necessary, or directly to a sound reproducer, such as a loud speaker, or the like.

The current and voltage impulses transmitted from the primary winding 2 to the secondary winding 3 are caused to influence a pair of electronic emission modulator tubes l and 8 which are placed in push-pull balanced arrangement. Each of the tubes has a heated cathode 9 or ID. They are also provided with a control electrode or grid H or 12, and an anode l3 or M. Adjacent the anodes there are respectively the suppressor grids l5 and I6 operating in a well known manner and connected to the cathodes 9 and [0. Intermediate the control electrodes and the suppressor grids are located the screen grid electrodes l1 and I8, which are used in a manner to be hereinafter described.

The terminals of the secondary winding 3 are connected respectively to the control electrodes The center of the winding 3 has a ground connection I 9. The input circuits for tubes 1 and 8 are completed through another ground connection 20, a cathode resistor 2|, and a connection 22 to the cathode 9 or ill. Thus, the input of the two tubes 1 and 8 are placed in a push-pull relationship.

The output circuits are also conventional and include connections from the terminals of primary winding 5 respectively to the anodes l3 and [4. A center connection 23 is made to the positive side of a source of electromotive force, such as a B-battery 24. The negative side of this battery has a ground connection 25. The output circuit thus includes the resistor 2i which is common to both the input and output circuits.

In order to modulate the output circuit with currents having tremolo frequency of from five to ten cycles per second, use is made of an oscillator tube 26. This oscillator tube has a heated cathode 21, a control electrode or grid 28, and an anode 29. This oscillator uses a phase shift between the grid 28 and the anode 29 for obtaining oscillations.

As is usual in phase shift oscillators, use is made of a plurality of capacitors 30, 3i, and 32 connected in series between the anode 29 and the grid 28. Intermediate these capacitors are the usual resistors 33, 34, and 35 that are grounded at 36. A bypass condenser 31 may also be provided between the grid 28 and the ground connection 36. Adjustment of the frequency is provided by varying the resistor 34 in a well understood way.

The plate or anode 29 of the oscillator 26 is connected to the positive side of the battery 24. The cathode 2'! is connected to the negative side of the resistor 2|. Accordingly, the input circuit of the oscillator 26 includes the resistor 2| which is common to the input and output circuits of the modulator tubes 1 and 8.

A tremolo frequency current produced by the oscillator 26 thus passes through the resistor 2|, and the electromotive force across this resistor, being impressed on the input circuits of tubes 1 and 8, causes a corresponding modulation of the output current through transformer 4.

The intensity of the tremolo effects is obtained by control of the screen grids l1 and I8. These screen grids are connected together by a high resistance 38 and may also be connected to ground through bypass condensers 39 and 40. The screen grid potentials with respect to the potentials of cathodes 9 and I determine the cation on the characteristic curve at which the tubes 1 and 8 operate. When the tubes 1 and 8 operate upon a straight portion of the characteristic curve, no modulation is effected. However, by varying the potential of the grids i1 and I8, the tubes may be caused to operate on that portion of the characteristic curve which is distorted, and modulations may then be transmitted.

Control of the potentials of electrodes i1 and I8 is provided by the addition of resistors 4!, 42 and 43 in series, between the positive terminal of battery 24 and a ground connection 44. A center tap 45 extends between the common terminals of resistors 4| and 42 to an intermediate portion of resistance 38. This tap is adjusted ing point of the modulation tubes 1 and 8 can be varied to portions of the characteristic curve of greater or less curvature, thereby increasing or decreasing the intensity or depth of tremolo.

If the screen grid voltage is increased through a certain range, the range of operation of the tubes 1 and 8 becomes more linear provided that the other circuit constants have been properly chosen to suit the tubes employed.

This causes the tremolo intensity to diminish. At the same time, the potential difference across the cathode resistor 2| will increase, due to the increased cathode current caused by the rise in screen voltage. Since this cathode resistor is also in the input or cathode circuit of the oscillator 26, the oscillator grid 28 becames increasingly negative, eventually stopping the tube 26 from oscillating altogether. In this way, the tremolo can be reduced to the vanishing point.

A reduction in the screen grid potentials operates to increase the intensity of the tremolo effects.

The inventor claims:

1. In a system for adding tremolo effects to audio frequency currents: an amplifier having an input circuit and an output circuit; a resistor common to both circuits; an oscillator having a control electrode and an anode; a circuit connecting said control electrode, anode, and resistor; and means for varying the current flow through the resistor.

2. In a system for adding tremolo effects to audio frequency currents: an amplifier having a cathode, a control electrode, an anode, and a supplemental grid; an input circuit including the control electrode and the cathode, as well as a resistor; an output circuit including the anode and said resistor; means for coupling a source of audio frequency to the input circuit; an oscillator having a control electrode and a cathode; a circuit connecting the oscillator electrodes in series with said resistor; and means for controlling the potential of the supplemental electrode.

3. In a system for adding tremolo effects to audio frequency currents; a push-pull amplifier system having a pair of tubes each provided with a cathode, an anode, a control electrode, and a screen grid; input circuits for the tubes, includ ing a resistor common to both circuits; output circuits for the tubes, also including the resistor; a phase-shift oscillator having an input circuit including the resistor; and means for adjusting the potential of the screen grids.

4. In a system for providing tremolo effects for electrically amplified musical signals: the combination of a push-pull electron tube amplifier having a cathode circuit; a tremolo frequency electron tube oscillator having a cathode circuit; a coupling resistor common to both cathode circuits; and means for controlling and varying the amplitude of tremolo modulation.

5. In a system for adding tremolo efi'ects to audio frequency signals: an amplifier comprising an input and output circuit and a vacuum tube, said tube having a screen grid; a tremolo oscillator circuit comprising a vacuum tube and having a cathode resistor, said resistor being connected in said input circuit, thereby modulating the output of said amplifier according to the oscillations thereon; and circuit means connected to said screen grid for selectively varying the operating characteristics of said vacuum tube, thereby controlling the intensity of tremolo oscillations in said output circuit.

6. In a system for adding tremolo effects to audio frequency signals: an amplifier comprising input and output circuits and a vacuum tube, said tube having a screen grid; a tremolo oscillator comprising a vacuum tube and having a cathode resistor, said cathode resistor being connected to said input circuit, thereby modulating the output of said amplifier according to the am plitudes of oscillations thereon; and circuit means connected to said screen grid for selectively varying the modulation of audio frequency signals by affecting the linearity of said amplifier tube, and eventually cutting off the generation of tremolo oscillations after said means have passed beyond a minimum tremolo position.

PAUL H. ROWE.

REFERENCES CITED UNITED STATES PA'I'ENTS Name Date McKellip et al. Jan. 25, 1945 Number 

